Demystifying Fracking Fluid

This is what fracking looks like. Image: Day Donaldson

Hydraulic fracturing fluid has two functions - to convey pressure into the surrounding rocks, causing the eponymous fracturing, and to deliver the “proppants” into these gaps, to hold them open once the pressure is released. There are additional challenges such as bacterial growth, deposition of dissolved particles and absorption of water by surrounding clays, all of which are managed using their own classes of additives. Much of my information is from an excellent paper which you can find here (PDF).

Gelling agents - these are added to increase the viscosity of the water, allowing the proppant particles to stay in suspension. With water on its own, the particles would be inclined to sink to the bottom, which would make them rather difficult to manoeuvre into the fractures. Often these are derived from guar or cellulose based compounds, both of which are naturally derived and considered to be non-toxic and biodegradable, and a good thing too since they are used in concentrations of up to 1000mgL-1.

Foaming agents - they perform many of the same functions as gelling agents, with the advantage that they reduce the amount of water required. Carbon dioxide or dinitrogen gas are injected into the gelling liquids, causing them to expand. They are also less readily absorbed by clay, preventing clays in the well from swelling up and obstructing the operation.

Friction reducers - water has a habit of hydrogen bonding to things, so friction reducers are sometimes used to reduce the surface tension. This allows for a reduction in obstruction of fractures (something which is a possibility with gels and foams). Polyacrylamide is a commonly used friction reduces, and has a low toxicity. However reaction through heat or UV can cause it to degrade into acrylamide, which is rather carcinogenic. The risk of this happening during the fracturing process are very low, and evidence would suggest that aerobic biodegradation of polyacrylamide after use doesn’t produce acrylamide either.

Crosslinkers and breakers - two sides of the same process, crosslinkers cause polymer gels to bind into larger molecules, increasing viscosity, while breakers do the opposite, breaking them down again and reducing viscosity. High viscosity helps to suspend and deliver the proppant particles to their destination, then breakers can reduce the viscosity and allow recovery of the fluid from said cracks, preventing them from getting “gummed up”. Lowering the viscosity also facilitates the removal of the fluid from the well. Crosslinkers often function best at a particular pH, so pH adjusting chemicals are often added to optimise their performance.

Biocides - bacteria get around, and their dastardly activities can obstruct fracking. Sulfate reducing and acid forming bacteria contribute to the degradation of mine casings and other important equipment, so they are despatched using biocides. The range of substances used is vast, and while most degrade fairly quickly, Quaternary ammonium compounds have been observed to stick around in wastewater for some time. What’s more, their persistence inhibits many of the bacterially facilitated wastewater treatments which may otherwise have been employed.

Corrosion inhibitors - it’s not just the bacteria which are at it, various chemicals, either added to the fluid or dissolved from the surrounding rock, can corrode the metal parts of the well. The selection of corrosion inhibitor depends on the geological and environmental characteristics of the operation, and some such as acetaldehyde and thiourea are suspected to be carcinogenic.

Scale inhibitors - suspended ions like to form into crystals when they come into contact with solid surfaces. Scale inhibitors block the molecular attachment sites on growing crystals, inhibiting their growth, and preventing them from blocking every pore or pipe that they come into contact with.

Iron control - some geological formations contain a lot of soluble iron ions, which end up being deposited elsewhere in the works, and causing much the same problem as the previously mentioned crystals. Iron control chemicals bind with these ions to prevent them from being deposited.

Clay stabilisers - clay absorbs water and swells, causing obstruction of the well, or the pores and fractures from which the hydrocarbons are meant to escape. To prevent this, clay stabilisers are added, which inhibit the ability of clay particles to bond to water. Tetramethyl ammonium chloride has long been used, and is highly toxic. However the use of the far less toxic choline chloride is increasingly being adopted.

Surfactants - selectively used to perform any number of functions previously mentioned, surfactants can be used to control viscosity and surface tension, as a biocide and a clay stabiliser, depending on the formula used.

But will it kill me / my cat? As you can probably infer from that list, there are many chemical additives with varying toxicity, selectively used in different combination. The same paper analysed the data of 81 known chemical additives in fracking operations and could only obtain toxicity information for around two thirds of those. Three category 2 oral toxins were identified (propargyl alcohol, tetramethyl ammonium chloride and thiourea), meaning that mammalian toxic doses are between 50 and 500mg/kg body mass. Ten more were identified as category 3 (500 - 5,000mg/kg). Realistically, this means that the potential toxicity from contamination will depend on the concentrations of chemicals used, and the degree of contamination. It’s hard to say definitively, but you probably wouldn’t want to drink fracking fluid for a laugh. As mentioned in the previous post, contamination of groundwater from fracking, especially after disposal in injection wells, is not unheard of (PDF), so environmental monitoring and dilligent disposal practices are incredibly important so that we hopefully don’t ever have to learn first hand whether it’s a risk or not.

Stay tuned for:

• Earthquakes!
• The potential impacts of fracking on the local community and landscape

Something in the water

So, water. Useful stuff. We can perhaps conclude that faulty mining well casing is a source of methane in drinking water, but what about that somewhat mysterious “fracking fluid”? The evidence for this one is not so clear cut.

Image: ProgressOhio

I should probably explain why I keep on calling them mysterious, even though we largely know what sort of additives they are likely to contain. In the United States, disclosure of the ingredients in fracking fluids by drilling companies is largely voluntary, and many additives are not disclosed due to commercial sensitivity. The industry backed website FracFocus allows for the submission of additives by drilling companies, but regulation does not mandate their disclosure and it is up to the companies to decide what and whether to submit. It should be noted though that in the UK, regulations oblige mining companies to disclose all additives.

Hydraulic fracturing tends to be performed at great depth, an average of around 2500m below ground in the US, and the pressurisation of the fluid takes place in small “sections” of the horizontal well. This allows for greater control of the pressure, which can be optimised for the surrounding geology. Consequently, the chances of fracking fluid finding their way into local groundwater sources is fairly low, as it would have to migrate through hundreds of meters of rock. However, the depth at which fracking takes place is a function of the geology, rather than a measure to protect groundwater, and may range from over 5000m to as little as 30m. While fracking is not frequently performed at such shallow depths, this is well within the range of groundwater.

Even with a close vertical proximity to groundwater, our primary concern is whether any fracking fluid is allowed to migrate far enough from the mining well to pose a contamination hazard. It’s in the interest of mining companies to closely monitor the extent of the fractures which they induce, as too extensive a fracture could result in the escape of the gas, and too small would mean that they won’t make the best possible return on their investment.

Broadly speaking, most investigations have failed to find evidence of the chemicals associated with fracking fluid in drinking water. However, under some geological conditions, there is some evidence (pdf) of migration from fracture sites into groundwater reserves.

The vast quantity of water used during a hydraulic fracturing operation has to be disposed of after use. Often it is sealed underground in an “injection well”, and left there. This is associated with another issue, as the less constrained injection of pressurised water has the potential to unleash seismic energy stored in the surrounding geology. There is evidence that this has happened(pdf) (we’ll look at this more thoroughly in a future post).

So what can we take away from this? Fracking fluid may indeed find its way into groundwater supplies, but only under specific geological circumstances. It would seem that the biggest issue is with injection wells, where companies dispose of used water, rather than the actual mining site, since they’ll generally be under higher pressure and for a longer duration. Also, earthquakes.

Next time:

• A little bit about the stuff they add to fracking fluids. I’ve been promising it for ages but I keep running out of words.
• How much water? That’s a lot of water.
• Earthquakes? I’d rather the ground didn’t move, thank you.

Frack Overflow

I'm no chemist, but I'm willing to go out on a limb and say that water shouldn't catch fire. A frequent image used by the anti fracking movement is that of people setting fire to their taps, with the implicit claim that this is the result of nearby fracking operations.



YouTube videos are about as anecdotal as evidence can possibly get, so I was quite happy to place a large mental asterisk beside the whole flaming tap debate, with a view to doing some more research before forming an opinion. To be frank, I was not expecting to find any particular correlation between flaming taps and local fracking operations.

A 2011 paper by Osborne et al. details the sampling of water from 60 drinking water wells, drawing from bedrock aquifers, in the vacinity of the Marcellus and Utica shale formations in North America, where extensive fracking has been undertaken. 51 of these samples contained methane gas in some quantity. Using isotopic ratios of 13C in methane, they deduced whether the source was sub-surface methanogenic bacteria, or if the isotope ratio matched that of thermogenic methane (of the "fossil" variety, which would suggest a relationship with local mining activities). For wells within 1km proximity of active mining sites, the isotope ratio strongly implicated thermogenic methane as the predominant source of contamination, with other wells showing primarily microbial methanogenic sources. The amount of methane present in those wells near active drilling was also an average of 17 times higher.

What's interesting is that the same study used isotope ratios to look for signatures of contamination by hydraulic fracturing fluids or deep brines (which would have lay otherwise undisturbed prior to being poked by a drill), and found no evidence of such contamination. This would suggest that methane was getting into the water by some means other than through fractures opened by the fracking process, as this would have probably been accompanied by these other contaminants. This makes some degree of sense, as the depth of drinking water wells was around 60 to 90m, while the hydraulic fracturing was taking place at between around 1000 and 2000m. That's a pretty large slab of rock. One possible explanation is that the hydraulic fracturing process caused perturbations in pockets of methane higher up in the geology, which then migrated to a level where it could interact with the water table. Perhaps a more concerning possibility is that methane escaped from the mining well itself, and laterally migrated into the water table.

Compared to the UK, the United States has a fairly unregulated mining industry, so the integrity of mining wells may not be monitored as closely as we might like. That's not to say that no such lapses could possibly happen under the regulatory framework of the UK (or anywhere else for that matter), or even that these callous frackers don't in fact go to extreme lengths to control for leaks (after all, they can't sell that methane if it escapes), but given the incentive for any company to attempt to minimise overheads as long as the regulator's head is turned the other way, this state of affairs leaves me deeply concerned. Perhaps a nice glass of flaming water will help me to relax.

We're not quite finished with water. Next blog will deal with those mysterious "fracking fluids" so stay tuned for:

• What do they put in that stuff anyway?
• Where do they get all that water from?
• What do they do with it after they're done with it? Are you sure it doesn't end up in my drinking water?

A matter of Frack

So, who’s here for a dry and technical account of industrial mining techniques? Please try to contain your excitement. If you’re good, I’ll even include some diagrams.

Hydraulic fracturing is an old technique. As I expect is the case with many of you, it came to my attention during around 2010 with media coverage of oil and gas prospectors Caudrilla drilling exploratory well in Lancashire (UK). They intended to apply recently developed techniques to access hydrocarbons which were previously economically unviable. The results of these explorations, the public reaction and how this shaped the UK’s policy on fracking, will be examined more thoroughly in a future post. For now, please don your PPE and be sure to stay with the group.

This is what a frack looks like. Borrowed from here

Hydraulic fracturing is the use of pressurised water (or other fluids) to increase the porosity of rock. Water is injected down a borehole (the hole from the surface, also called the well) and the pressure is increased until it overcomes the structural integrity of the rock. This is manifested in the formation of various small cracks, radiating from the borehole. The purpose of this is to increase the exposed surface area of rock, and to give the gas (or oil, or water, although we’re primarily concerned with gas in this series) more gaps to migrate into the borehole for collection. Suspended in the fluid are tiny “proppants” such as sand particles, which prop open the cracks once the pressure is released, otherwise the ambient pressure would cause them to close again. The advantage of this is that very “tight” hydrocarbon reservoir rocks, which would otherwise be reluctant to give up their charge, can be stimulated into producing more of the good stuff. Conventional hydrocarbon sources are generally porous rocks, those with plenty of escape channels for hydrocarbons to migrate through. It’s only with recent advances that it’s become economically viable to extract hydrocarbons from the less forthcoming rock types such as shale, which is generally very finely grained and tightly packed.

Fundamentally, these are the important ingredients for hydraulic fracturing, but as with virtually every other industrial technique, some of the world’s finest minds have endeavoured to optimise the heck out of it.

To this end, a variety of chemicals are added to the fluid, to modify its properties and increase its efficacy. These include gelling and foaming agents, which help to keep the proppants in suspension, as well as various classes of chemicals to, for example, prevent deposition of dissolved compounds. While it may be slightly terrifying to think of an intangible concoction of chemicals being injected into the ground in vast quantities, it’s worth considering that only around 0.05% of the injected fluid is made up of these chemicals. However 0.05% of between 7600 and 18,899m3 of fluid is still pretty vast. The important questions are whether they can end up in the surrounding environment or the water supply, and what sort of harm they could do if they did. Furthermore, it’s worth considering whether any of the hydrocarbons which are released from the fractured rock are likely to end up where they shouldn’t.

As I previously insinuated, fracking is not a new phenomenon. The technique was developed in the 1940s and has been used extensively, in order to stimulate low permeability rocks into giving up their precious hydrocarbons, or to simply increase the yield of the not-so-low permeability rocks of more conventional sources. The recent explosion of fracking has resulted from techniques which allow for previously nonviable sources to be tapped more effectively (referred to as “unconventional” hydrocarbon sources).

Horizontal drilling has been used to increase the area of contact between mining wells and the hydrocarbon bearing rock. To understand why, we need to talk about rocks. Hold onto your hats, people.

Horizontal layers of rock. Picture of the Lias
Shale Group, taken by me near Lyme Regis in 2014

One of the fundamental principles of geology is superposition; when rock forms from compaction (a process called diagenesis), it tends to be oriented the same way as the ground (that is to say, relatively flat for the most part). When more rock forms, it tends to form in the same orientation, superimposed on top of that previous rock. This results in the “layer cake” pattern that you might see in cliff faces, where many layers have been serially compacted into layers of rock. These layers are referred to as beds, and lots of geologically similar beds are referred to as a formation. The upshot of this is that hydrocarbon bearing rocks tend to form vast subterranean sheets, horizontally oriented. Consequently, a horizontal mining well can follow the sheet and maximise the amount of contact with the hydrocarbon bearing rock.

So, let’s recap:

• Hydraulic fracturing is the use of a pressurised liquid to force open cracks in a non porous rock.
• Proppants are little “support strut” particles which are forced into the cracks, to hold them open once the pressure is released.
• Chemical additives are used to change the properties of the water, making the process more effective.
• Unconventional hydrocarbon sources are increasingly getting the fracking treatment, where previously it would not have been economically viable.
• Horizontal drilling allows for maximum exchange between the formation containing the hydrocarbon and the mining well.
• I stole that “layer cake” comparison from the Hitchhiker's Guide to the Galaxy.

I don’t suggest you go out and attempt your own frack based upon the information contained in this post, as it’s a very brief overview of the aspects concerned, but it should serve as a starting point for our more thorough investigation of some of the specific issues surrounding the process, and the reasons for social and political reactions to this expansion of fracking in recent years.

Next time:

• Where does all that water come from?
• Where does all that water go?
• Will it kill my cat/make me sterile?
• Who do I blame if my taps catch fire?

Fracking Agnosticism

Fracking is a tricky one for me. The part of me which is inclined to wear the occasional sandal recognises the issues with encouraging the use of any additional fossil fuel resources, especially when the government appears to have a will to move away from renewables. The many anecdotal reports of environmental damage resulting from hydraulic fracturing, such as groundwater contamination and earthquakes, not to mention the inevitable greenhouse gas emissions, give this side of me pause. After all, I quite like the environment.

A slightly more pragmatic internal voice screams about the economic benefit of domestic fuel production and independence from some slightly undesirable political regimes from whom we currently get our fix. Doubtless, the majority of objections are from the same people who don't want wind farms within ten miles of their houses, as they will "detrimentally impact the character of the landscape".


A third voice in my increasingly crowded psyche has only the most fleeting regard for the opinions of the other two. Its only desire is to see the peer reviewed scientific paper pertaining to the matter at hand, such as whether there is any statistical data to support anecdotal reports of groundwater contamination, and whether the particular mechanisms employed in fracking can be responsible. It also has some rather scathing things to say about the feasibility of Star Trek, but I'll save that for another blog.


I intend for this blog to strike a balance between these often contradictory perspectives, with a particular view to finding the empirical evidence behind the various claims surrounding fracking, if indeed such evidence exists. As a UK citizen I will have a particular focus on the matters of policy and geology which pertain to this green and largely pleasant land, with reference to other countries where fracking has already been employed more extensively. Perhaps by the end of this I'll even be bold enough to give up my fracking agnosticism and form a real opinion.


Stay tuned for the next exciting instalment, where you will be treated to such joys as:

• Fracking! What actually is fracking? How does one "frack?" 
• Shale gas! Where would I get this shale gas from? How did it get there in the first place?